This invention relates to functionalized polymers.
Synthetic polymers are generally characterized as either resinous or elastomeric. Historically, elastomeric polymers required chemical vulcanization before they possessed sufficient strength for utilities such as tire treads, shoe soles, rubber bands, and other elastic utilities requiring some level of strength. However, these compositions after vulcanization were no longer thermoplastic.
In the 1960s a major advance in the art occurred with the discovery and commercialization of thermoplastic elastomers. These materials possess an internal elastomeric block and a plurality of terminal aromatic blocks. On cooling from a melt, such compositions exhibit high tensile strength, high elongation, and rapid and almost complete recovery after elongation. This is attributed to the fact that in the bulk state, the aromatic end segments of these block copolymers agglomerate. At temperatures significantly below the glass transition temperature (T.sub.g) of the aromatic end blocks, these agglomerations (domains) act as strong, multifunctional junction points and so the copolymers behave as though they are joined in a cross-linked network.
Such polymers are non-polar and hence are sometimes not ideally suited for applications that require adhesion to polar substrates or that require compatibility with polar polymeric materials. This can be overcome by incorporating a functional group on the polymer. However, these polymers contain a large amount of aliphatic unsaturation in the diene blocks which can result in cross-lining and gellation of polymer chains during the free-radical grafting reactions used to incorporate polar functional groups. Hence, it is necessary to utilize a hydrogenation step prior to incorporating a functional group. Hydrogenation can be accomplished using any of several hydrogenation processes known in the art. For instance, the commonly used method is to employ a Group VIH metal catalyst, particularly nickel or cobalt, with a suitable reducing agent such as an aluminum alkyl to catalyze the hydrogenation. The disadvantage in this is the necessity for the additional hydrogenation and catalyst removal steps. These steps are equipment and time intensive and thereby increase the complexity and cost of producing functionalized thermoplastic-plastic elastomers. In addition, the hydrogenation catalysts are sensitive to certain poisons, making hydrogenation of polymers containing particular functional groups or coupling agent residues difficult or impossible.
Thus, it would be highly desirable to have a process by which functionalized thermoplastic elastomers could be directly produced without the necessity of a hydrogenation step.